In most jurisdictions, for example under the GDPR and certain US state laws, you have the right to data portability and can export the data from your current period tracker to keep a copy.
For information on how to export, check out the settings or support pages of your current app. Make sure to export before you delete your account.
Right now, it’s not possible to import such data files directly into Clue. But an import feature could be introduced in the future.